When an oil well is drilled, drilling fluids are pumped downhole. The drilling fluids serve several purposes. One purpose is to lubricate the drill bit. Another purpose is to carry cutting from away from the drill bit. Yet another purpose is to control pressure within the wellbore.
Papers have documented that these drilling fluids damage the formation by adversely effecting its relative permeability. At an annual technical meeting of the Petroleum Society of CIM in Calgary, May 9-12, 1993 one such paper, paper no. CIM 93-24, was presented entitled "Reductions in the Productivity of Oil and Gas Reservoirs due to Aqueous Phase Trapping". This paper outlines mechanisms leading to aqueous phase trapping which are caused by the introduction of fluids into the well.
The recognition of this problem has lead to various methods being developed to stimulate oil or gas wells. These methods are used to stimulate a well prior to it being put into production or when production is falling below levels that make the recovery of the oil or gas commercially viable. The most common method of stimulating a well prior to it being put into production is acidizing a well through the use of a "stimulation fluid". U.S. Pat. No. 5,152,907 which issued to Amoco Corporation in 1992 entitled "Solvent Systems for Use in Oil and Gas Wells" provides background relating to the composition of such stimulation fluids. It should be noted, however, that Paper no. CIM 93-24, lists among the fluids that cause formation damage through aqueous phase trapping, stimulation fluids (including spent acid).
There are various forms of venturi-style pumping apparatus that are presently used for cleaning sand from horizontal sections of unconsolidated reservoirs or pumping from vertical sections of said reservoirs. One example of such a pumping apparatus is U.S. Pat. No. 5,033,545 which issued to Sudol in 1991.